feat(Calendar): update today cell style

[ArgoZhang]

Link issues

fixes #7356

Summary By Copilot

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• Merge the latest code from the main branch

Summary by Sourcery

Update Calendar component styling to improve the visual treatment of the current day and selected dates, including dark theme support.

New Features:

• Add a distinct circular border style for the today cell when it is not selected in the Calendar view.

Enhancements:

• Adjust Calendar selected date colors to use a solid primary background with white text, with a separate color for dark theme.
• Introduce dedicated SCSS variables for today border color and dark-theme selected background in the calendar.
• Simplify month and week navigation handlers by using conditional expressions instead of branching logic.
• Remove obsolete table cellpadding/cellspacing attributes from Calendar markup for cleaner HTML.

[sourcery-ai]

Reviewer's Guide

Updates Calendar component styling to improve today/selected cell visuals (including dark theme), slightly refactors month/week navigation logic, and cleans up some Razor/table attributes and comments.

File-Level Changes

Change	Details	Files
Refine calendar CSS variables and today cell styling, including dark-theme support.	Introduce a dark-theme override for calendar selected background using a new CSS variable mapped to the dark theme token. Extend calendar CSS variable set to include today border color, and wire it to the SCSS variable. Change default selected color to white and selected background to a solid primary color; add dedicated dark background token for selected state. Style the today cell by adding a positioned span with a circular border pseudo-element that renders when the cell is today but not selected.	src/BootstrapBlazor/Components/Calendar/Calendar.razor.scss src/BootstrapBlazor/wwwroot/scss/variables.scss
Minor behavioral refactor of calendar month/week navigation methods.	Simplify OnChangeMonth to use a conditional expression while preserving behavior of resetting to today on zero offset and otherwise shifting by months. Simplify OnChangeWeek similarly to use a conditional expression while preserving behavior and updating WeekNumberText and ValueChanged notifications.	src/BootstrapBlazor/Components/Calendar/Calendar.razor.cs
Small markup and comment cleanups in Calendar component.	Remove obsolete cellspacing and cellpadding attributes from calendar tables, relying on class-based styling instead. Adjust or localize summary XML comment for the Calendar component and normalize file headers and namespace line BOM usage.	src/BootstrapBlazor/Components/Calendar/Calendar.razor src/BootstrapBlazor/Components/Calendar/Calendar.razor.cs src/BootstrapBlazor/wwwroot/scss/variables.scss

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#7356	Make the Calendar's is-today styling visually obvious so that the cell representing today is clearly distinguishable from other days (including the same day number in other months).	✅

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[sourcery-ai]

Hey - I've left some high level feedback:

• The new today cell ring styles use several hard-coded pixel/rem units for size and offsets (width: 2rem, top: -6px, left: -8px), which may not scale well with different font sizes or layouts; consider centering the circle relative to the span (e.g., with top: 50%, left: 50%, transform: translate(-50%, -50%)) or using em-based values to make it more robust.
• To keep theming concerns localized and easier to maintain, consider nesting the dark theme variable overrides inside the existing .calendar block (e.g., .calendar[data-bs-theme='dark'] { --bb-calendar-selected-bg: ... } or similar) instead of having a separate [data-bs-theme='dark'] .calendar block at the top.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new today cell ring styles use several hard-coded pixel/rem units for size and offsets (`width: 2rem`, `top: -6px`, `left: -8px`), which may not scale well with different font sizes or layouts; consider centering the circle relative to the span (e.g., with `top: 50%`, `left: 50%`, `transform: translate(-50%, -50%)`) or using `em`-based values to make it more robust.
- To keep theming concerns localized and easier to maintain, consider nesting the dark theme variable overrides inside the existing `.calendar` block (e.g., `.calendar[data-bs-theme='dark'] { --bb-calendar-selected-bg: ... }` or similar) instead of having a separate `[data-bs-theme='dark'] .calendar` block at the top.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (add522a) to head (7d9d34b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #7381   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          748       748           
  Lines        32776     32764   -12     
  Branches      4546      4546           
=========================================
- Hits         32776     32764   -12     

Flag	Coverage Δ
BB	100.00% <100.00%> (?)

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[Copilot]

Pull request overview

This PR updates the Calendar component's today cell styling to use a circular border indicator instead of just color highlighting. The changes improve visual distinction between today's date and selected dates while adding dark theme support for the selection styling.

Key Changes:

• Introduced a circular border around today's date (visible only when not selected)
• Updated selected cell colors to use white text on blue background for better contrast
• Added dark theme support for selected cells
• Refactored navigation methods to use ternary operators for conciseness

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/BootstrapBlazor/wwwroot/scss/variables.scss	Added new SCSS variables for today's border color, updated selected cell colors, and introduced dark theme variant for selected background
src/BootstrapBlazor/Components/Calendar/Calendar.razor.scss	Implemented dark theme support, added circular border styling for today's cell using CSS pseudo-element, and registered new CSS variables
src/BootstrapBlazor/Components/Calendar/Calendar.razor.cs	Added Chinese documentation comment for the component and refactored month/week navigation methods to use ternary operators
src/BootstrapBlazor/Components/Calendar/Calendar.razor	Removed deprecated HTML attributes (cellspacing and cellpadding) from table elements

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[Copilot]

The border circle uses hardcoded pixel values for positioning (top: -6px, left: -8px) and dimensions (width: 2rem, height: 2rem). This creates a tight coupling between the pseudo-element size and position. Consider using CSS variables or calc() to make the positioning relative to the element's dimensions, or add a comment explaining these magic numbers to improve maintainability.