Add form styles and update button classes for consistency

- Introduced a new CSS file for form styles (forms.css) to enhance form layout and design.
- Removed deprecated button styles from imports.css and updated button classes across templates to use the new utility classes.
- Updated various templates to reflect the new button styles, ensuring a consistent look and feel throughout the application.
- Refactored form-related styles in main.css and removed redundant styles from projects.css and scenarios.css.
- Ensured responsive design adjustments for form actions in smaller viewports.

templates/exports/modal.html

@@ -9,7 +9,7 @@
         <h5 class="modal-title">Export {{ dataset|capitalize }}</h5>
         <button
           type="button"
-          class="btn-close"
+          class="btn btn--ghost btn--icon"
           data-dismiss="modal"
           aria-label="Close"
         ></button>
@@ -40,10 +40,10 @@
           >
         </div>
         <div class="modal-footer">
-          <button type="button" class="btn btn-secondary" data-dismiss="modal">
+          <button type="button" class="btn btn--secondary" data-dismiss="modal">
             Cancel
           </button>
-          <button type="submit" class="btn btn-primary">Download</button>
+          <button type="submit" class="btn btn--primary">Download</button>
         </div>
         <p class="form-error hidden" data-export-error></p>
       </form>